feat: Cloudflare Turnstile on auth, CSP fixes, admin/SEO/analytics additions

Turnstile bot protection (sign-in, sign-up, password-reset):
- Register Better Auth's captcha plugin with the cloudflare-turnstile
  provider; endpoints listed explicitly rather than relying on defaults.
  /reset-password is intentionally excluded — it is reached only via a
  single-use emailed token.
- Add an explicit-render Turnstile widget component. Tokens are single-use,
  so each form resets the challenge after a failed submit; submit stays
  disabled until a token is held.
- Read the site key server-side and pass it down as a prop, so rotating it
  does not require a rebuild.
- Fail fast in production when TURNSTILE_SECRET_KEY is missing, and when a
  secret is set without a site key (that combination would demand a token
  no form can produce, locking every user out).
- Pass a throwaway secret during `next build` in the Dockerfile, mirroring
  the existing BETTER_AUTH_SECRET treatment, so image builds don't need it.

CSP fixes in middleware (these blocked Turnstile entirely):
- Add frame-src for challenges.cloudflare.com. Without it the widget's
  iframe fell back to default-src 'self' and was blocked outright.
- Allow 'unsafe-eval' and websockets in DEVELOPMENT only. `next dev`
  compiles with eval(), so the strict policy threw EvalError and killed
  hydration — no client JS ran at all, which also meant form submit
  handlers never fired. Production policy is unchanged and still strict.

Also included (concurrent work in the tree):
- Admin organizations pages and lib/admin/orgs.
- Episode moderation migration, SEO metadata (sitemap, robots, JSON-LD,
  OG/Twitter images, manifest), Umami analytics, not-found page.

Local dev database: docker-compose.dev.yml provisions Postgres 18 on port
5443 (5432-5442 are in use by other local projects).

Note: `npx tsc --noEmit` currently fails in app/(app)/team/page.tsx — an
`invitations` prop the component does not accept. This predates the commit
and will fail `next build` until fixed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

components/auth/sign-in-form.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState } from "react";
+import { useRef, useState } from "react";
 import Link from "next/link";
 import { useRouter, useSearchParams } from "next/navigation";
 import { Loader2 } from "lucide-react";
@@ -12,23 +12,42 @@ import { Card, CardContent, CardHeader, CardTitle, CardDescription } from "@/com
 import { signIn } from "@/lib/auth/auth-client";
 import { safeRedirect } from "@/lib/utils";
 import { GoogleButton } from "./google-button";
+import { Turnstile, type TurnstileHandle } from "./turnstile";
 
-export function SignInForm({ googleEnabled }: { googleEnabled: boolean }) {
+export function SignInForm({
+  googleEnabled,
+  turnstileSiteKey,
+}: {
+  googleEnabled: boolean;
+  turnstileSiteKey: string | null;
+}) {
   const router = useRouter();
   const params = useSearchParams();
   // Validate the ?redirect param to prevent open-redirect attacks.
   const redirectTo = safeRedirect(params.get("redirect"));
   const [loading, setLoading] = useState(false);
+  // Turnstile is only rendered when configured; when it is, a solved token is
+  // required before the form can be submitted. The server rejects a missing or
+  // reused token regardless, so this is UX, not the security boundary.
+  const [captchaToken, setCaptchaToken] = useState("");
+  const turnstileRef = useRef<TurnstileHandle>(null);
+  const captchaRequired = !!turnstileSiteKey;
 
   async function onSubmit(e: React.FormEvent<HTMLFormElement>) {
     e.preventDefault();
     setLoading(true);
     const form = new FormData(e.currentTarget);
-    const { error } = await signIn.email({
-      email: String(form.get("email")),
-      password: String(form.get("password")),
-    });
+    const { error } = await signIn.email(
+      {
+        email: String(form.get("email")),
+        password: String(form.get("password")),
+      },
+      captchaRequired ? { headers: { "x-captcha-response": captchaToken } } : undefined
+    );
     if (error) {
+      // Turnstile tokens are single-use — issue a fresh challenge for the retry,
+      // otherwise the next submit fails verification instead of on credentials.
+      turnstileRef.current?.reset();
       toast.error(error.message ?? "Invalid email or password");
       setLoading(false);
       return;
@@ -71,7 +90,20 @@ export function SignInForm({ googleEnabled }: { googleEnabled: boolean }) {
             </div>
             <Input id="password" name="password" type="password" autoComplete="current-password" required />
           </div>
-          <Button type="submit" className="w-full" disabled={loading}>
+          {turnstileSiteKey && (
+            <Turnstile
+              ref={turnstileRef}
+              siteKey={turnstileSiteKey}
+              onToken={setCaptchaToken}
+              onError={() => toast.error("Could not load the security check. Please refresh.")}
+              className="flex justify-center"
+            />
+          )}
+          <Button
+            type="submit"
+            className="w-full"
+            disabled={loading || (captchaRequired && !captchaToken)}
+          >
             {loading && <Loader2 className="h-4 w-4 animate-spin" />}
             Sign in
           </Button>